But after a number of off-field incidents the Wallaby ace, who was won 44 caps for his country, found himself without a contract for his country for the upcoming 2014 season.
And as a result O'Connor has come to England and the Exiles in a bid to rediscover his best form, and nail down the No.15 jersey.
"Having decided that I needed a change from both a personal and playing point of view, I spoke to clubs in Japan and France and concluded that the best way forward for my development was to move to England," said the versatile 23-year-old.
"I want to develop into a world-class 15. I've played all over the park which has been a good thing for me, that utility ability has got me into a lot of teams.
"But at the same time I haven't been able to nail down one position. It's always been my goal to be a world-class player in one position.
"And away from the field I need to find balance in certain ways. I've been in bit of a bubble in the last six years.
"I've enjoyed it and wouldn't take anything back, it's been an amazing ride. Every opportunity to pull on that gold jersey has been awesome."
And Irish director of rugby, Brian Smith, described O'Connor as the "most significant signing in the club's history".
"His signing is the injection of class we need," Smith said. "James is a world-class player and a terrific kid and it is fantastic to have him at London Irish.
"He will bring a huge amount of experience to our group and will fit in well to our style of play. He is fit and ready to play so the coaching group will get him up to date on everything and hopefully he'll be ready to go this weekend."